With the development and deployment of wireless networking devices such as laptop computers, personal digital assistant devices, etc. and infrastructures, consumers and businesses are increasingly being able to realize the benefits of true mobile computing, collaboration, and information exchange. No longer are business travelers required to carry an assortment of cables and search endlessly for an available data port simply to connect to a network to retrieve email messages, download files, or exchange information. No longer are companies and home consumers restrained in where they may access their networks by the location of the Ethernet jacks on the wall. Meeting participants and groups of friends may now form their own ad hoc networks without connecting cables between themselves or logging in to some preexisting network. They can log onto the network using a wireless protocol while running on battery power, thereby allowing even greater mobility
However, while the concept of mobile computing on wireless networks is well accepted, the implementation of this concept has taken on many forms. That is, there now exists several different wireless protocol standards that are competing in the marketplace. These standards include 802.11b (also know as Wi-Fi for wireless fidelity), 802.11a (also know as Wi-Fi5), 802.11g, HomeRF, Bluetooth, Wireless 1394, HiperLAN2, UWB, ZigBee, etc. Each of these different standards have particular advantages and were and are being developed with particular applications and users in mind. One thing in common with these standard is the use of a wireless network interface card (NIC).
As mobile workers demand greater mobility, both inside the organization and when traveling, the mobile workers are limited by the lifetime of the battery powering the wireless device. The battery life is a major restriction on mobility. The wireless NIC is the third highest consumer of battery power in a laptop. In small form factor devices, the wireless NIC consumes a larger percentage of battery power than in a laptop. Most of that energy is used for wireless data transmissions. Since the amount of power a battery provides is limited, how to minimize power consumption to extend the operation time of the device powered by the battery is an important issue for those devices.
One of the functions the wireless NIC performs is scanning to determine which devices are in the range of the wireless networking device. A principle rationale for scanning is to migrate from one network to another network that is more preferred. For example, a more preferred network may be cheaper to operate than the other network. Existing services command the wireless NIC to perform a scan after a fixed period of time (e.g., 60 seconds) elapses regardless of what is going on. Each scan consumes power. There is no intelligence as to whether the device is associated, connected for the last hour, is sending traffic at the time the scan is starting, etc. This pollutes the radio space and wastes battery power. For example, if there are 300 stations and each one is scanning every 60 seconds, on average five stations will be running scans every second. When a scan is started on a network channel, a probe request is sent and other devices on the network channel cannot transmit while a device transmits the probe request. When devices see the probe request, the device that would respond to the probe request transmit a probe response, which in-turn consumes available time to transmit on the network channel. As a result, each time a scan is run, a slice of the available time to transmit on the network channel is taken away. If there are a number of devices scanning unnecessarily, the total time available is reduced and power is wasted.